The Snell U.S. Pat. No. 2,812,185 issued Nov. 5, 1957 describes a centerless grinding machine having a magnetic driver for holding the workpart during grinding. The machine includes a rotatable spindle mounted in a housing by anti-friction bearings and having a cantilevered end extending outside the housing. Mounted on the cantilevered end outboard of the anti-friction bearings is the magnetic driver assembly engaging the workpart. The assembly includes inter-fitting face pieces provided with a magnetic flux by an annular magnet and pair of pole pieces inside the assembly. The magnet and pole pieces are axially movable inside the assembly to divert flux from the workpart to facilitate its removal after grinding.
More recently, grinding machines have employed an electro-magnetic driver in which an annular electro-magnet coil is mounted to the stationary machine housing around the cantilevered end of the rotatable spindle. The driver that engages the workpart is attached to the spindle end and rotatable therewith. As in the grinding machine described in the aforementioned Snell U.S. Pat. No. 2,812,185, the coil and driver are located outboard from the spindle anti-friction bearings outside the machine housing.
The grinding machines described having the magnet or electro-magnet coil disposed outboard from the spindle bearings outside the machine housing suffer from several disadvantages. In particular, the magnet or electromagnet and any associated couplings are interposed between the spindle bearings and workpart driver. This increases the distance between the workpart driver and bearings and thus accentuates undesirable movement of the workpart driver due to any imperfections in the spindle bearings and their alignment. Of course, this further translates into undesirable movement of the workpart during the grinding operation. Also, the size and cost of the grinding machine are increased as a result of interposing the magnet or electro-magnet between the spindle bearings and workpart driver.